Do a google search for disease resistant apple trees. Also look for Miller Nurseries, as I think they sell four varieties (jonafree, macfree) of disease resistant. The last thing you want to do is spray the trees (IMO). Now disease resistance does not mean disease free but it helps.
There is a variety named Haralson http://www.minnesotaharvest.net/appleharalson.htm
that was developed in Minnesota so its winter hardiness should not be a concern in southern Iowa. Why I suggest this variety is that it is known for setting heavy fruit loads, so much that it breaks limbs. Since this tree would not need to look pretty, I think a few broken limbs could be tolerated for the heavy production. Some apple trees tend to alternate yearly between heavy and light yields. You might want to try to find out if the variety is a consistent producer.